LUBRICATING DEVICE AND METHOD

Field of the Invention

This invention relates to the lubrication of compression ignition (diesel) engines. In particular, though not exclusively, this invention relates to adjusting cylinder lubricant feeds in slow- and medium- speed diesel engines, such as for example those used in marine, railway or stationary applications.

Background to the Invention

Slow-speed diesel engines typically operate at less than about 300 rpm, e.g. in the range of about 50 to 250 rpm, usually with a high peak power output per cylinder, e.g. in the range of from 2000 to 6000 kW per cylinder. Slow-speed diesel engines are typically 2-stroke engines and may be, for example, of crosshead construction, direct coupled and direct reversing. Typically such engines comprise a separation, such as a diaphragm and stuffing boxes, separating power cylinders from a crankcase, to prevent combustion products from entering the crankcase and mixing with crankcase oil. Slow-speed diesel engines tend to use significant amounts of sulphur-containing fuel, such as residual fuel oil.

Medium-speed diesel engines operate in the range of from about 300 to 1000 rpm and can provide moderate to high peak power outputs per cylinder, for example up to about 2000 kW per cylinder. Such engines may be 4-stroke or 2-stroke engines and may also run on sulphur- containing fuel, such as residual fuel oil.

The cylinders of slow- or medium-speed diesel engines are lubricated by cylinder lubricant. To counteract corrosion by acidic sulphur species, cylinder lubricants are provided with an alkalinity reserve defined by the Total Base Number (TBN) , generally expressed in mg KOH/g and measured according to ASTM D2896. For example, it is common to provide slow-speed 2-stroke compression ignition engines with cylinder lubricant having a TBN in the range from 40 to 100 mg KOH/g, such TBN being achieved through the inclusion of additives in a lubricant base stock.

In slow- or medium-speed engines, engine operating temperatures and pressures tend to break down lubricant films on the internal walls of engine cylinders, which can result in increased wear. Cylinder lubricants are thus supplied substantially continuously at a lubricant feed rate. The lubricant feed rate is generally

expressed in g/kW h, i.e. as a function of the power output of the engine.

It is known to adjust cylinder lubricant feed rates in heavy diesel engines not only in response to power output but also in response to engine loading conditions, sulphur content in the fuel, or particular engine designs. This allows the lubricant feed to be optimised for better engine performance.

US Patent Application 2003/0196632 Al discloses a method to employ instrumentation to effectuate variation in lubricant flow rate or properties in response to actual engine conditions. The method regularly monitors one or more engine parameters with instruments such as XRF to determine wear metals or IR for base number measurement. The measured engine parameters are used to calculate the feed rate of lubricant to the engine.

It is also known that the sulphur content of fuel can also have an impact on lubrication requirements. The combustion of higher sulphur fuels often produces higher emissions of sulphur oxides, nitrogen oxides and

particulate matter such as soot and metal oxides . With lower sulphur fuels, slow- or medium-speed diesel engines may be able to operate with a reduced lubricant feed rate and/or with a lower TBN. In such an event, excessive amounts of unreacted compounds in an additive package providing TBN, such as over-based detergents, can contribute to the formation of deposits. Accordingly, it is known to vary the TBN of cylinder lubricant to match the sulphur content of fuel.

Adjustments to the lubricating composition can be made following periodic review or continuously, on-board.

US 2003/0159672 Al discloses a method of regularly monitoring one or more engine parameters of an all-loss lubricating system and calculating from the engine parameters an amount of a secondary fluid that is required to be added to a base lubricant to create a modified base lubricant that is applied to the engine during operations.

US 2006/0068995 Al discloses a method of creating a cylinder oil, the method comprising modification of at least one initial fluid by determining the TBN(s) of the at least one initial fluid, determining a desired TBN of a cylinder oil and adjusting the TBN(s) of the at least one initial fluid accordingly by blending the at least one initial fluid with suited additive (s) .

US 2008/0318818 Al discloses a method of lubricating a marine diesel 2-stroke engine which involves monitoring performance characteristics of an engine and preparing an appropriate lubricant composition by in-situ blending of at least two different fluids, one of which comprises an additive package with detergents.

Despite these developments, operational problems related to cylinder lubrication continue to arise, such as hitherto unexplained scuffing or excessive corrosive wear .

It is an aim of the invention to provide an improved solution for lubricating diesel engines operating on sulphur-containing fuel, particularly diesel engines of the slow- and medium-speed type, and/or to solve at least one problem associated with the prior art.

Statements of the invention

According to a first aspect of the invention there is provided a method of lubricating a diesel engine operating on sulphur-containing fuel, the method

comprising supplying a feed of lubricant to a cylinder of the diesel engine, wherein the feed is adjusted based on the humidity of intake air of the engine.

It has been found that the degree of humidity of the intake air for combustion of sulphur-containing fuel in diesel engines has an effect on the depletion of the TBN of lubricants fed to the cylinders of such engines.

The humidity of the intake air of the engine may be determined or inferred in any suitable manner and the method may comprise measuring or monitoring the humidity accordingly. The humidity may be the absolute humidity or relative humidity. In one embodiment of the present invention, the feed of lubricant is adjusted based on the absolute humidity. In another embodiment of the present invention, the feed of lubricant is adjusted based on the relative humidity, in particular at a given air

temperature. Any measurement representative of intake air humidity may be used to adjust the feed of lubricant.

Conveniently, the humidity of the intake air may be measured or monitored by a humidity sensor. For

particular accuracy, the humidity of the intake air may advantageously be measured or monitored in a scavenge air space of the engine.

The feed of lubricant can be adjusted across the whole range of relative (0-100%) or absolute humidity of the intake air measured at any specific intake air temperature (°C).

In an embodiment the adjustment based on humidity is calibrated by one or more previous measurements on drained oil samples. For example, the method may comprise a preliminary step of measuring the TBN and/or metal content of drained oil samples at a plurality of humidities, to calibrate the adjustment based upon humidity .

Regular measurements may be taken to monitor, estimate or infer the humidity over a period of time e.g. for at least 5 minutes, at least 10 minutes, at least 1 hour or at least 1 day.

As can be seen from the non-limiting example illustrated in Figure 1, at a given engine load, fixed fuel sulphur content and fixed lubricant feed rate, the relationship between the depletion of the alkaline reserve (Base Number) and the intake air humidity was found to follow a linear relationship, with a lower alkaline reserve (Base Number) being observed at a higher humidity.

The present invention allows lubricant feeds to be optimised for better performance by taking into account the factor of the humidity of the intake air. However, the feed of lubricant may also be adjusted based on other factors in addition to the humidity of the intake air.

In an embodiment, the method additionally comprises adjusting the lubricant feed based on one or more factors selected from the power output of the engine and/or each cylinder, engine load, sulphur content of the fuel used by the engine, the TBN of the lubricant, wear, deposits, and/or corrosion.

In an embodiment, the feed is adjusted (or

maintained) as a function of the humidity of the intake air, over a period of time, e.g. for at least 5 minutes, at least 10 minutes, at least 1 hour or at least 1 day.

The feed may be adjusted by varying the feed rate and/or the composition of the feed. Thus, the feed rate function of the humidity of the intake air.

In an embodiment, the feed rate is adjusted within the range of from about 0.50 to about 1.4 g/kW h (i.e. g/h per kW of engine power) . In an embodiment, the feed rate is adjusted within the range of from about 0.50 to 1.2, about 0.5 to 1.1, about 0.6 to 1.4, about 0.6 to

1.2, or about 0.6 to 1.1 g/kW h. The particular level of the feed rate will depend on the engine type and may take into account other factors, for example those listed above .

In one embodiment the feed rate is adjusted to tend towards a higher feed rate when the humidity of the intake air increases. In one embodiment the feed rate is adjusted to tend towards a lower feed rate when the humidity of the intake air decreases. The term "tend towards" reflects that other factors, such as those listed hereinabove, may optionally also be used to adjust the feed rate and may hence affect the overall

adjustment. The particular weighting given to the humidity of the intake air to optimise performance may depend on the engine type.

The feed may additionally or alternatively be adjusted by varying its composition or content. In an embodiment the concentration of an additive providing an alkalinity reserve may be varied in the feed.

In one embodiment a blend-on-board system may be employed to effect variations in the content of the feed. An example of a blend-on-board system is described in US 2006/0068995 Al .

In an embodiment, the method comprises the steps of: (1) monitoring the humidity of the intake air for the engine; (2) selecting a lubricant to modify the

performance characteristics of the engine, wherein the lubricant is prepared by in-situ controlled blending of at least: (i) an additive providing an alkalinity reserve, and optionally other performance additives, and (ii) a base oil of lubricating viscosity; and 3)

supplying the lubricant prepared in step (2) to the engine .

Controlled blending may be carried out by any known blending process known in the art, provided the amounts of additive are metered to provide the lubricating composition required.

In an embodiment, the additive comprises one or more overbased detergents and/or one or more neutral

detergents as will be described below.

In an embodiment, the lubricant is prepared by blending of more than two different base oils, additives, fluids or components. In an embodiment, the number of base oils, additives, fluids or components ranges from 2 to 8, 2 to 6, 2 to 4, 3 to 8, 3 to 6, or 3 to 4. In an embodiment the number of additives, fluids or components is 3.

The particular number, nature and concentration of additives, fluids or components may be selected

consistent with achieving desired properties of the lubricant feed. For example, the nature, number and concentration of additives, fluids or components may be selected to provide a lubricant feed as described anywhere herein.

In one embodiment the concentration of an additive providing an alkalinity reserve is adjusted to tend towards a higher TBN in the feed when the humidity of the intake air increases. In one embodiment the

concentration of the additive is adjusted to tend towards a lower TBN in the feed when the humidity of the intake air decreases. The term "tend towards" reflects that other factors, such as those listed hereinabove, may optionally also be used to adjust the concentration of the additive and may hence affect the overall adjustment. The particular weighting given to the humidity of the intake air to optimise performance will depend on the engine type.

In principle, the benefits of the invention may be expected to apply broadly to any diesel engine operating on sulphur-containing fuel. However, the present invention was conceived in the context of marine diesel engines which tend to operate on residual fuel oils with high sulphur content and may be subject to significant humidity variations. The advantages of the invention may be noticeable and beneficial particularly in embodiments in which the engine is a slow- or a medium-speed diesel engine, e.g. as described or defined hereinabove. In an embodiment the engine is a 2-stroke diesel engine, in particular a marine 2-stroke diesel engine. In an embodiment, one or more cylinders of the engine are total-loss lubricated by the lubricant feed.

The diesel engine operates on sulphur-containing fuel. Such operation may occur concurrently with adjustment of the lubricant feed, but the invention also embraces methods where such operation occurs before or after adjustment of the feed, e.g. during a period of 24 or 48 hours after the beginning or end of adjustment. In particular, the invention embraces methods in which a fuel substantially free from sulphur or fuel with a lower sulphur content than the sulphur-containing fuel is used temporarily, for example when a marine engine enters a port or inland water. Relevant exemplary categories of fuel are defined below.

The sulphur-containing fuel may in principle be any fuel containing at least a detectable amount of sulphur, e.g. greater than 1 ppm. In an embodiment the fuel comprises a middle distillate and/or a residual oil. In an embodiment the sulphur-containing fuel comprises at least 0.0001% w/w sulphur. Such levels might be found even in ultra low sulphur fuels, such as Ultra Low

Sulphur Marine Gas Oil (ULSMGO) . In another embodiment the fuel comprises at least 0.001% w/w sulphur. Such levels may be found even in low sulphur fuels, such as Low Sulphur Marine Gas Oil (LSMGO) . In yet another embodiment the fuel comprises at least 0.1% w/w sulphur, or even at least 0.5% w/w, or at least 1.0% w/w, at least 2%, or at least 3% sulphur. Such levels might be found, for example, in Low Sulphur Intermediate Fuel Oil (e.g. LS 180 or LS 380) . In yet a further embodiment the fuel comprises at least 3.5% w/w sulphur. Such levels might be found, for example, in Intermediate Fuel Oil (e.g. IFO 380) . In general, fuel with a higher sulphur content is lower in cost. The present invention is of particular advantage in engines running on lower cost fuels. The effect of intake air humidity on lubricant performance is believed to be particularly pronounced where fuels with higher levels of sulphur are used. Thus the invention advantageously enables a solution to a hitherto perceived trade-off between cost and corrosion.

The lubricant may be any lubricant suitable for lubricating the engine, in particular engine cylinders. In an embodiment the lubricant is as defined anywhere in

WO 99/64543 Al, the content of which is incorporated herein by reference.

In an embodiment the lubricant is an SAE 40 grade or SAE 50 grade or SAE 60 grade lubricant.

As aforesaid, the lubricant may be pre-blended or blended on board or in-situ by mixing. In an embodiment the lubricant comprises at least one base oil and at least one additive, which may constitute an additive package. The base oil may optionally also contain one or more pre-blended additives.

In an embodiment, the base oil or combination of base oils has a viscosity ranging from 2 mm ² /s to 40 mm ² /s or to 50 mm ² /s (at 100° C) . Suitably, the base oil may comprise new (i.e. fresh or unused) system oil, used system oil (may also be referred to as light neutral base oil) , heavy neutral base oil, bright stock, or mixtures thereof. Such oils include natural and synthetic oils, oil derived from hydrocracking, hydrogenation, and hydrofinishing, unrefined, refined and re-refined oils and mixtures thereof. Hydrotreated naphthenic oils are also known and can be used, as well as oils prepared by a Fischer-Tropsch gas-to-liquid synthetic procedure as well as other gas-to-liquid oils.

As aforesaid, the additive or additive package may comprise one or more overbased detergents and/or one or more neutral detergents.

In an embodiment, the lubricant which is supplied to the cylinders has a TBN (mg KOH/g) ranging from 20 to 100. In an embodiment, the lubricant has a TBN of 20 to 80, 20 to 70, 30 to 100, 30 to 80, 30 to 70, 40 to 100, 40 to 80, or 40 to 70.

In an embodiment, the overbased detergent has a TBN of at least 200. In an embodiment, the overbased detergent has a TBN of at least 230 or at least 300. In an embodiment, the overbased detergent has a TBN of up to 600, 550 or 500. Examples of ranges of TBN for the overbased detergent include 200 to 600, 200 to 550, 200 to 500, 230 to 600, 230 to 550, 230 to 500, 300 to 600,

300 to 550, and 300 to 500.

In an embodiment, the neutral detergent has a TBN of less than 200. In an embodiment, the neutral detergent has a TBN of less than 175. Examples of ranges of TBN for the neutral detergent include 1 to 200, 1 to 175, 20 to

200, and 20 to 175.

In an embodiment, the one or more overbased

detergents or one or more neutral detergents comprise a salicylate, a sulphonate, a phenate or a mixed substrate detergent. The mixed substrate detergent can, for example, comprise a complex/hybrid of a sulphonate and a phenate, optionally in the presence of a salicylate.

In an embodiment, other additives are also present in the lubricant feed. In an embodiment the lubricant feed comprises a polymeric thickener or viscosity index improver. The polymeric thickener may, for example, include styrene-butadiene rubbers, ethylene-propylene copolymers, hydrogenated styrene-isoprene polymers, hydrogenated radical isoprene polymers,

poly (meth) acrylate acid esters, polyalkyl styrenes, polyolefins (such as polyisobutylene) ,

polyalkylmethacrylates and esters of maleic anhydride- styrene copolymers . In an embodiment, the polymeric thickener has a weight average molecular weight (Mw) of at least 8000, at least 8400, at least 10,000, at least 12,000, at least 15,000, at least 20,000, at least 25,000, at least 30,000 or at least 35,000. The polymeric thickener generally has no upper limit on Mw, however in an embodiment the Mw is less than 2,000,000, less than 500,000, less than 300,000, less than 150,000 or less than 75,000.

In an embodiment, the lubricant which is applied to the engine comprises at least one performance additive selected from the group consisting of metal deactivators, dispersants, antioxidants, antiwear agents, corrosion inhibitors, antiscuffing agents, extreme pressure agents, foam inhibitors, demulsifiers, friction modifiers, pour point depressants and mixtures thereof.

In an embodiment, the lubricant comprises an antiwear agent such as for example a metal hydrocarbyl dithiophosphate . Examples of a metal hydrocarbyl dithiophosphate include zinc dihydrocarbyl

dithiophosphates (often referred to as ZDDP, ZDP or ZDTP) . Examples of suitable zinc hydrocarbyl

dithiophosphates compounds include the reaction

product (s) of butyl/pentyl, heptyl, octyl, nonyl

dithiophosphoric acids zinc salts or mixtures thereof.

In an embodiment, the antiwear agent is ashless, i.e. the antiwear agent is metal-free. In an embodiment the metal-free antiwear agent is an amine salt. The ashless antiwear agent may contain an atom including sulphur, phosphorus, boron or mixtures thereof.

In an embodiment, the lubricant comprises a

dispersant. The dispersant may be an ash-containing dispersant or an ashless-type dispersant, the latter being so named because, prior to mixing with other components of the lubricant, they do not contain metals which form sulfated ash. After admixture, they may acquire metal ions from other components; but they are still commonly referred to as "ashless dispersants" . The dispersant may be used alone or in combination with other dispersants. In an embodiment, the ashless dispersant does not contain ash-forming metals. Ashless type dispersants are characterised by a polar group attached to a relatively high molecular weight hydrocarbon chain. Ashless dispersants may include an N-substituted long chain hydrocarbon succinimide such as alkenyl

succinimide. Examples of N-substituted long chain alkenyl succinimides include polyisobutylene succinimide with number average molecular weight of the

polyisobutylene substituent for example from 350 to 5000, from 350 to 3000, from 500 to 5000, or from 500 to 3000. Succinimide dispersants and their preparation are disclosed, for example, in US 4234435. Succinimide dispersants are typically the imide formed from a polyamine, typically a poly (ethyleneamine) .

In an embodiment, the lubricant feed comprises an antioxidant, such as for example a diphenylamine , a hindered phenol, a molybdenum dithiocarbamate, a

sulphurised olefin and mixtures thereof. In an

alternative embodiment the lubricant is free of an antioxidant .

In an embodiment, the lubricant feed may also comprise other performance additives, such as for example: corrosion inhibitors such as for example octylamine octanoate; condensation products of dodecenyl succinic acid or anhydride and a fatty acid such as oleic acid with a polyamine; metal deactivators including derivatives of benzotriazoles, 1, 2, 4-triazoles, benzimidazoles, 2-alkyldithiobenzimidazoles or 2- alkyldithiobenzothiazoles ; foam inhibitors including copolymers of ethyl acrylate and 2-ethylhexylacrylate and optionally vinyl acetate; demulsifiers including trialkyl phosphates, polyethylene glycols, polyethylene oxides, polypropylene oxides and (ethylene oxide-propylene oxide) polymers; pour point depressants including esters of maleic anhydride-styrene, polymethacrylates ,

polyacrylates or polyacrylamides ; and/or friction modifiers including fatty acid derivatives such as amines, esters, epoxides, fatty imidazolines,

condensation products of carboxylic acids and

polyalkylene-polyamines and amine salts of

alkylphosphoric acids.

The total combined amount of the additives present may for example be from 0 to 25, from 0 to 20, from 0 to 15, from 0 to 10, from 0.01 to 25, from 0.01 to 20, from 0.01 to 15, from 0.01 to 10, from 0.05 to 25, from 0.05 to 20, from 0.05 to 15, from 0.05 to 10, from 0.1 to 25, from 0.1 to 20, from 0.1 to 15, from 0.1 to 10, from 0.5 to 25, from 0.5 to 20, from 0.5 to 15, or from 0.5 to 10 weight percent of the total lubricant.

From a second aspect, the invention resides in a lubricating system for a diesel engine operating on sulphur-containing fuel, the system comprising:

a humidity sensor for sensing the humidity of intake air of the engine;

a feed adjustment unit for controlling a feed of lubricant to one or more cylinders of the engine; and an engine control unit configured to control the feed adjustment unit based on the humidity sensed by the humidity sensor.

In this second aspect of the invention, the humidity of intake air may be the absolute or relative humidity of the intake air.

In an embodiment the feed adjustment unit comprises a unit for controlling a feed rate of the lubricant and/or a blending unit for controlling the composition of the lubricant .

In an embodiment the system is configured and fitted to perform a method in accordance with the first aspect of the invention.

From a third aspect, the invention resides in a computer-readable medium containing programming

instructions that cause a computer processor to perform the steps of a method in accordance with the first aspect of the invention.

From a fourth aspect, the invention resides in a kit of a computer-readable medium according to the third aspect of the invention and one or more of (i) a cylinder lubricant, e.g. as defined anywhere herein; and (ii) a system according to the second aspect of the invention. Advantageously, the computer-readable medium of such a kit may be particularly tailored to the lubricant and/or system of the kit. The kit may be provided as a bundle with instructions for combined use or its components may be sold separately but with instructions for combined use.

From a fifth aspect, the invention resides in a method of counteracting increased corrosion and/or deposits in a cylinder of a diesel engine operating on sulphur-containing fuel, the increased corrosion and/or deposits being those resulting from a variation ( i . e .

increase or decrease) in the humidity of intake air of the engine, the method comprising adjusting a feed of lubricant supplied to the cylinder based on the humidity of intake air of the engine. In this fifth aspect of the invention, the humidity of intake air may be the absolute humidity of intake air or the relative humidity of intake air .

From a sixth aspect, the invention resides in the use of an amount of alkalinity reserve in a lubricant for the purpose of tailoring the lubricant to compensate for an intake air humidity in an engine in which the

lubricant is or is to be used. In this sixth aspect of the invention, the intake air humidity may be absolute humidity or relative humidity.

Throughout the description and claims of this specification, the words "comprise" and "contain" and variations of the words, for example "comprising" and "comprises", mean "including but not limited to", and do not exclude other moieties, additives, components, integers or steps. Moreover the singular encompasses the plural unless the context otherwise requires: in

particular, where the indefinite article is used, the specification is to be understood as contemplating plurality as well as singularity, unless the context requires otherwise .

Preferred features of each aspect of the invention may be as described in connection with any of the other aspects. Generally speaking the invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any

accompanying claims and drawings) . Thus features, integers, characteristics, compounds, chemical moieties or groups described in conjunction with a particular aspect, embodiment or example of the invention are to be understood to be applicable to any other aspect,

embodiment or example described herein unless incompatible therewith. Moreover unless stated

otherwise, any feature disclosed herein may be replaced by an alternative feature serving the same or a similar purpose .

Where upper and lower limits are quoted for a property, then a range of values defined by a combination of any of the upper limits with any of the lower limits may also be implied.

In this specification, references to component properties are - unless stated otherwise - to properties measured under ambient conditions, ie at atmospheric pressure and at a temperature of from 16 to 22 or 25°C, or from 18 to 22 or 25°C, for example about 20°C.

The present invention will now be further described with reference to the following non-limiting examples, and the accompanying illustrative drawings, of which:

Figure 1 is a graph showing the effect of variations in the humidity of the intake air for combustion of sulphur containing fuel in a large 2-stroke marine diesel engine on the depletion of the TBN of cylinder lubricant; and Figure 2 is a schematic view of a lubricating system in accordance with an embodiment of the invention.

Example 1 - Effect of humidity of engine intake air on TBN

Investigations were carried out with commercially available 70 TBN cylinder oil (Shell Alexia 50) .

Alkaline reserve depletion was studied as a function of absolute humidity contained in the intake air (at various temperatures) for scavenging at engine load ranging from 65 to 85% MCR in a 96 cm cylinder bore 2- stroke marine diesel engine at two different levels of fuel sulphur. As is common in the art, the absolute feed rate of lubricant was continuously adjusted based on engine load. The feed rate relative to engine load was kept constant at 0.9 g/kWh.

It was found that the relative humidity of intake air has an influence in the depletion of TBN of the lubricant, as can be seen in Table 1 and Figure 1.

In accordance with the invention the cylinder lubricant feed rate could be further optimised for better performance if the humidity of the intake air for combustion is considered in controlling the feed rate (typically together with sulphur content, load, and any other particular engine characteristics) .

Table 1 - Effect of humidity of intake air on TBN

MCR 65-85% MCR 65-85%

S% = 2.2-2.4 S% = 2.8-3%

Air Relative Absolute TBN remaining Air Relative Absolute TBN

Temperature Humidity Humidity in cylinder Temperature Humidity Humidity remaining

(°C) (%) [g/m ³ ] lubricant (°C) (%) [g/m ³ ] in

drain oil [mg cylinder

KOH/g] lubricant drain oil

[mg

KOH/g]

23 67 13 81 35 09 4 67 4.27 26. 68

23 67 13 81 34 81 4 67 4.27 27. 16

23 67 13 81 36 58 4 67 4.27 31. 19

23 67 13 81 37 65 4 67 4.27 31. 56

24 83 18 12 31 71 11 87 8.92 23. 18

24 83 18 12 30 46 11 87 8.92 24. 44

24 83 18 12 33 73 11 87 8.92 25. 47

24 83 18 12 34 99 11 87 8.92 24. 87

29 78 22 50 29 29 27 68 17.6 20. 70

29 78 22 50 28 16 27 68 17.6 18.88

29 78 22 50 30 83 27 68 17.6 18. 23

29 78 22 50 29 84 27 68 17.6 18. 93

Example 2 - Controlling lubricant feed based on humidity

Referring now to Figure 2, a lubricating system 1 for a 2-stroke marine diesel engine 2 comprises an engine control unit 4, a humidity sensor 6, an on-board

lubricant blending system 8 and a feed control 10.

The 2-stroke marine diesel engine 2 is of

conventional slow-speed type. A humidity sensor 6 is installed in the scavenge space of the engine to measure the humidity of the intake air of the engine.

The humidity sensor is connected to the engine control unit 4, which is programmed to control operation of the engine, though such control may also be carried out by a separate unit if desired. The engine control unit 4 may comprise or be connected to a user interface (not shown) for displaying engine operating conditions and/or receiving user inputs. It may also receive further information, e.g. about power output of the engine or each cylinder, engine load, sulphur content of the fuel used by the engine, the TBN of the lubricant, wear, deposits, and/or corrosion, from additional sensors or modules (not shown) .

The engine control unit 4 comprises a

microprocessor. The engine control unit controls the operation of the on-board blending system 8, which is in fluid communication with sources (e.g. tanks) of base oil

12 and first and second additives 14, 16. The first additive 14 comprises an overbased detergent. The second additive 16 is optional and comprises a performance additive package. Based upon commands from the engine control unit 4, the blending system 8 blends base oil and optionally one or more of the additives 14, 16 to provide a cylinder lubricant 18.

The feed control 10 receives the lubricant 18 blended by the blending system 8 and, based upon commands from the engine control unit 4, supplies lubricant 18 to the cylinders of the engine 2 as a feed 20 having a feed rate determined by the engine control unit 4.

In operation, the system 1 is set to deliver lubricant composition 18 to the cylinders of the engine at a feed rate. The humidity sensor 6 continuously monitors the humidity of intake air and feeds this information to the engine control unit 4.

Where an increase in humidity is detected by the sensor 6, the engine control unit is programmed to perform one or both of the following by providing appropriate commands to the feed control unit 10 and/or blending system 8:

(i) increase the TBN of the lubricant 18 by

increasing the concentration of alkalinity reserve additive 14 in the lubricant 18;

(ii) increase the feed rate of the feed 20 of the lubricant 18.

Where a decrease in humidity is detected by the sensor 6, the engine control unit is programmed to perform one or both of the following:

(i) decrease the TBN of the lubricant 18 by

decreasing the concentration of alkalinity reserve additive 14 in the lubricant 18;

(ii) decrease the feed rate of the feed 20 of the lubricant 18.

In a variant of this embodiment the engine control unit is additionally programmed to take into account one or more of power output of the engine or each cylinder, engine load, sulphur content of the fuel used by the engine, the TBN of the lubricant, wear, deposits, and/or corrosion in controlling the blending system 8 and feed control 10.

In a further variant of this embodiment the blending system 8 is omitted.